Passat 96, TD Umwelt overheating

[the_old_diver]

These things always happen on a Saturday afternoon.

I fitted a new radiator to my Passat yesterday and after a short test drive I left it running in the drive. After about 10 mins I noticed water dripping and saw hot water coming out of the expansion / header tank. I also noticed that the radiator fans were not turning. After letting it cool I added some more water and tried to diagnose the problem.

When I remove the 3-terminal plug from the sensor screwed into the side of the rad I read 12 volts across some of the pins (I forget which) and when I short them out the radiator fans starts to work.

Would I be right in deducing that the sensor in the radiator - which I changed over from the old rad - is probably defective, or are there other possible causes for non rotation?

Thanks in advance. OD

[the_old_diver]

OK, Saturday has come round again. I have just fitted the radiator fan switch to the radiator I bought last week radiator £75 :-), switch £25 :-( and the blessed engine is now blowing water out of its expansion tank even before the temp gets to an indicated 90 - odd. The fan does run though, so that is some progress.

I am inviting ideas as the what causes this water loss through what I assume is a pressure relief valve under a black fig-leaf of a cover on the outboard side of the cream coloured expansion tank.

I have considered a blown cylinder head gasket, but the pressurisation and water loss doesn't happen straight away after a cold start, but only after a few minutes of running, and there is no smell of exhaust gas in the vicinity.

I have considered a failed or nearly failed water pump, allowing hots spots to develop in the head which causes localised boiling and expulsion of not-boiling water from the expansion tank.

And I have also considered that maybe the pressure relief valve - if such it be - is itself faulty and causing the water loss.

Does anyone have any other ideas or preferences from my own list?

Thanks in advance. OD

[adamss24]

Did you bleed the cooling system ? You may have an air lock in the heater matrix wich does not allow water to flow thus making it boil. The thermostat does not oppen then and thats why the fan does not kick in.

[the_old_diver]

Thanks for that, Mr A.
I haven't bled the heater matrix because the only hose connections I could see were higher up than the expansion tank, and there was hot-ish air coming out of the heater when I tried it. I did make a point of having the heater set to Hot while doing the filling so the supply valve would be open.

Should I slacken and try to vent at the radiator top hose connection after putting as much in the expansion tank as will go, to try to get more burps from the rad?

Does anyone have a copy of the official written procedure for refilling? It shouldn't be rocket science for a marine engineer but it is proving a bit of a tease :confused:

Cheers, OD

[the_old_diver]

Problem found!
The filler cap on the expansion tank has its "working parts" hidden away from view, but the barrier between the inside and the outside is an O-ring type seal about 3mm from the open end of the filler cap.

If you look at the photo you can see the golden coloured O-ring sitting nicely in its groove, arrowed "Good" on the left, and mangled and displaced, labelled "Bad" on the right.

The car was lying 10 miles in one direction from my home, and the parts shop 10 miles in the opposite one so in the interests of time versus money I bought a new filler cap for £12 rather than buy a new O-ring, only to find it wasn't exactly the right section or material for the 110C and 29 psi.

Engine now pressurises - probably for the first time in ages, and I have one or two new minor leaks, but at least the head gasket is still intact.

Lesson learned? Blowing water out of the expansion tank isn't always terminal - check the filler cap!

Hope this helps someone. OD